A cold cathode electron beam gun also called an E-beam gun can be used to improve the operation of a CO.sub.2 laser. The CO.sub.2 laser includes a tubular envelope containing the gas at one atmosphere or more. There are parallel spaced electrodes inside the envelope that are oriented longitudinally. A fast discharge between electrodes is required for proper functioning of the CO.sub.2 laser and for longer operating life of the laser. The driving pulse needs to be as short as possible to minimize the likelihood that any hot spot between electrodes will avalanche to a high current hard arc. Preionization of the gas between electrodes contributes to a more uniform discharge. One method of preionization is to pulse an E-beam gun directed transverse to the main electrodes and between the full length of the electrodes. A well defined pulse shape, i.e., approximately rectangular with a nearly flat top, is required. The gun resistance varies during the pulse length from infinity at the start of a driving pulse to several ohms at the end of the driving pulse. Thus driven, the gun delivers a ramp current rising from zero. It may be required to operate single-shot or at a regular repetition rate. Voltage across the E-beam gun must be unidirectional to avoid arcing.
Volume 5 of the Radiation Laboratory series published by McGraw-Hill, and entitled "Pulse Generators", provides background information on line-type pulsers, referred to hereafter as line-type modulators or modulators that can be used to drive an E-beam gun. Energy is stored electrostatically or magnetically and all of the stored energy is discharged into the load during each pulse under the control of a switch that is closed for a length of time corresponding to pulse duration and is open for at least the interpulse time required to store the same amount of energy for the next pulse. The load impedance and the network impedance are equal for optimum power transfer. A well-defined pulse is delivered by the pulse forming network. Load voltage is equal to one-half the voltage of the energy storing network immediately prior to a pulse. However, if a load of variable impedance such as an E-beam gun for driving a laser or a crossed-field amplifier for a radar, is connected across a line-modulator pulse forming network of constant impedance, the impedance mismatch causes damaging voltage reflections as well as varying voltage across the load. High voltage operation can exacerbate the problem. One illustration is a pulse source that can provide a pulse of about two microseconds, that is substantially flat and on the order of 250,000 volts, and that supplies ramp current during the pulse rising from zero to about 20,000 amperes and at a repetition rate on the order of 50 hertz, for operating an E-beam gun for a CO.sub.2 laser.